This relates generally to electronic devices, and more particularly, to electronic devices with displays.
Electronic devices often include displays. For example, cellular telephones and portable computers often include organic light-emitting diode displays for presenting visual information to a user.
To ensure that organic light-emitting diode displays do not consume too much power, electronic devices often use a peak luminance control algorithm (sometimes referred to as automatic current limiting). When this functionality is enabled, the peak luminance of displayed images is limited whenever the content being displayed exhibits large values of average luminance. When the average luminance of a frame of image data is low, the display is allowed to display content with a large peak luminance. In this situation, a display with sparse content such as a few icons on a black background can display the content brightly.
When the average luminance of a frame of image data is high, there is a potential for excessive current draw by the display if all of the content in the frame is displayed at maximum luminance. When the peak luminance control algorithm is used, the peak luminance of the content is reduced automatically by the display. This ensures that the amount of current and therefore the amount of power that is drawn by the display will be capped. In addition to limiting power consumption, this may help limit temperature rise in the display and thereby help extend the lifetime of display pixels in the display.
Manually and automatically controlled display brightness settings also are used to adjust how brightly organic light-emitting diode displays operate. Organic light-emitting diode displays produce light by applying current to emissive organic materials. Conventionally, analog data signals are driven to corresponding thin-film transistors that pass the current to the emissive organic materials. The analog data signals are typically derived based on a set of reference voltages values, which are calibrated for specific display brightness settings. The display may include a display driver having a cascaded gamma circuit for generating the set of reference voltage values.
In particular, the display brightness settings can be adjusted to dim the brightness of the display by scaling the references voltages using the cascaded gamma circuit. As the voltage scales, the display needs to be re-calibrated to maintain the accuracy of the color that is being displayed. When a user of the displays adjusts the display brightness settings to intermediate levels that are between the calibrated brightness settings, the reference voltage values may be interpolated from the calibrated settings. In particular, the interpolation is performed in the digital domain. Because of the cascaded structure of the gamma circuit, digital interpolation introduces errors that can ripple and accumulate across the reference voltages, which can lead to luminance jumps (especially at low dimming levels) and unexpected color shifts in the display.